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Identifying Alkenes with Bromine Water

Feb 9, 2025

Testing for the Presence of an Alkene

Key Concepts

  • Alkenes

    • Contain a carbon-carbon double covalent bond.
    • Known as unsaturated hydrocarbons.
    • Double bond can break in an addition reaction allowing two new atoms to join.
  • Alkanes

    • Saturated hydrocarbons with no double bonds.
    • No addition reactions due to lack of double bonds.

Characteristics

  • Both alkanes and alkenes are colorless liquids (e.g., hexane and hexene).

Bromine Water Test

  • Bromine Water

    • A solution of bromine dissolved in a solvent, appearing orange or yellowy brown.
  • Reactions with Alkenes

    • Alkenes can undergo an addition reaction with bromine water due to unsaturation.
    • Double bond in alkenes (e.g., hexene) breaks, allowing bromine atoms to add across the bond.
    • Product formed: Dibromoalkane (colorless).
    • With excess alkene and small bromine water, solution turns from brown to colorless.
  • Reactions with Alkanes

    • Alkanes are saturated; thus, no addition reaction occurs with bromine water.
    • Solution remains brown as no reaction takes place.

Summary

  • Alkenes: Unsaturated, can react with bromine water to change color from brown to colorless.
  • Alkanes: Saturated, do not react with bromine water; solution remains brown.